The proposed experiments focus on the area of the mediobasal hypothalamus which is the final common neural pathway before release of hypothalamic tropins into the pituitary portal blood system. Anatomical techniques will use converging methods consisting of Golgi silver chromate impregnations, horseradish peroxidase filling, and electron microscopy. Combinations of these three techniques will facilitate examination of the intrinsic neural circuits of the medial hypophysiotrophic area (HTA) which includes the arcuate and the suprachiasmatic nuclei. Local axons will be studied, as well as the possibility of gap junctions and dendrodendritic synapses. The distribution of neurons which maintain axon terminals in the median eminence will be studied with retrograde transport of horseradish peroxidase from the median eminence. Further attention will be directed to subpopulations of cells within the hypohysiotrophic area.